The plant hormone jasmonic acid (JA) controls diverse aspects of host immunity and development. Studies with the model plant Arabidopsis thaliana and tomato (Solanum lycopersicum) indicate that the E3 ubiquitin ligase SCFCOI1 is strictly required for transcription of jasmonate-responsive genes. JAZ (JAsmonate ZIM-domain) proteins repress the expression of jasmonate-responsive genes by interacting with the basic helix-loop-helix transcription factor MYC2. In response to a jasmonate signal, JAZ proteins are subject to SCFCOI1-mediated ubiquitination and subsequent degradation by the 26S proteasome. Binding of JAZ repressors to the F-box protein COI1 is stimulated by the JA-amino acid conjugate jasmonoyl-isoleucine (JA-Ile). Coronatine, a toxin produced by plant disease-causing pathogens, strongly promotes COI1-JAZ interactions. The proposed research will use Arabidopsis and tomato as experimental model systems to develop the hypotheses that COI1 is a receptor for JA-Ile and coronatine, and that JAZ repressor proteins determine the specificity by which SCFCOI1 controls the diversity of jasmonate-regulated processes. A combination of biochemical, genetic, and cell biological approaches will be used to address the following specific aims: 1) To determine the role of COI1 and JAZ in binding jasmonate ligands;2) To measure the endogenous level of JA-Ile and other JA-amino acid conjugates in healthy, wounded, and diseased tissues;3) To determine the physiological function of JAZ family members;4) To identify regions in the Cterminal domain of JAZ repressors that interact with COI1 and MYC2;and, 5) To determine the role of JAZ-JAZ dimerization in regulating jasmonate responses. This research will contribute broadly to an understanding of the molecular mechanisms by which lipid-derived hormones control developmental and immune function in multicellular organisms. Crosskingdom conservation of components of the jasmonate signaling cascade indicates that the research will provide insight into signaling processes that are conserved between plants and animals. The paradigm of ligand-mediated SCF-substrate recognition that has emerged from plant hormone research establishes a novel mechanism for sensing small molecules in biological systems, which may have far-reaching implications for medicine and human health, including potential new avenues for developing drugs that target E3 ubiquitin ligases in humans. The recent discovery of jasmonates as anti-cancer agents indicates further that the proposed research is relevant to the discovery of novel therapeutic agents against neoplastic disease. Finally, the work will reveal the molecular mechanism by which a pathogenic microbe co-opts signaling pathways in its eukaryotic host during disease. The proposed research on the mechanism of jasmonate signaling will contribute broadly to an understanding of how lipid-derived hormones control developmental and immune function in diverse multicellular organisms, ranging from plants to humans. The study of ligand-mediated recognition of target substrates by E3 ubiquitin ligases will provide new information on how small molecules mediate proteinprotein interactions in biological systems, which may have far-reaching implications for medicine and human health, including potential new avenues for developing drugs that target E3 ubiquitin ligases in humans. PUBLIC HEALTH RELEVANCE: The proposed research will reveal the molecular mechanism by which a pathogenic microbe coopts signaling pathways in its eukaryotic host during disease, and is also relevant to the discovery of novel therapeutic agents against neoplastic disease.